Lymphoblastoid Cell lines: a Continuous in Vitro Source of Cells to Study Carcinogen Sensitivity and DNA Repair

Obtaining a continuous source of normal cells or DNA from a single individual has always been a rate limiting step in biomedical research. Availability of Lymphoblastoid cell lines (LCLs) as a surrogate for isolated or cryopreserved peripheral blood lymphocytes has substantially accelerated the process of biological investigations. LCLs can be established by in vitro infection of resting B cells from peripheral blood with Epstein Barr Virus (EBV) resulting in a continuous source, bearing negligible genetic and phenotypic alterations. Being a spontaneous replicating source, LCLs fulfil the requirement of constant supply of starting material for variety of assays, sparing the need of re-sampling. There is a reason to believe that LCLs are in close resemblance with the parent lymphocytes based on the ample supporting observations from a variety of studies showing significant level of correlation at molecular and functional level. LCLs, which carry the complete set of germ line genetic material, have been instrumental in general as a source of biomolecules and a system to carry out various immunological and epidemiological studies. Furthermore, in recent times their utility for analysing the whole human genome has extensively been documented. This proves the usefulness of LCLs in various genetic and functional studies. There are a few contradictory reports that have questioned the employment of LCLs as parent surrogate. Regardless of some inherent limitations LCLs are increasingly being considered as an important resource for genetic and functional research.

in use from last few decades with minimal amendments providing an excellent model system with various benefits as LCLs. LCLs are relatively easy to prepare and the maintenance is effortless.
They also exhibit minimum somatic mutation rate in continuous culture (4).They provide an unlimited source of biomolecules like DNA, RNA or proteins and are a promising in vitro model system for genetic screening studies, genotype-phenotype correlation studies, a variety of molecular and functional assays related to immunology and cellular biology studies (5-8).
Besides this, utility of LCLs has been fully exploited mainly in studies where a single sample is required for a variety of assays. In such cases,   (2,20). In addition, a second glycoprotein gp42 binds to human leukocyte antigen HLA class II molecule as co-receptor (2,21). Through these interactions, the fusion machinery is triggered and the viral membrane fuses with the endosomal membrane to release viral genetic materials inside the cell. EBV infection in other cell types, mainly epithelial cells, is less efficient and occurs through poorly defined separate pathways (21). This difference in cell tropism can be attributed, to some extent, to the type of cell from which viral preparations are made (21).

Utility of lymphoblastoid cell lines for genetic and functional studies
The property of LCLs to be able to grow in continuous culture together by maintaining a close similarity to the starting parent lymphocytes has been very well exploited in various studies leading

Fig 3. Trend of usage of human EBV LCLs in last one decade
Usage of EBV LCLs for carcinogen sensitivity, DNA damage/repair and other studies has been consistent throughout the years. Solid region in the graph represents reports where EBV LCLs are used as a model system. Shaded region represents other EBV LCLs reports. Black Line above shaded region represents total available EBV LCLs reports in each year.

Fig 4. Average distribution of human EBV LCLs for various studies in last one decade
A major segment of the available reports where EBV LCLs are used as a model system comprises of cytotoxicity and DNA damage/repair studies. Blue region in the graph represents reports where EBV LCLs are used as a model system for DNA damage repair studies (15%). Red region represents other cytotoxicity studies (29%). Green region represents other studies utilising EBV LCLs model system (56%).   (Fig.2).
As seen from published literature, EBV LCLs have been utilized throughout the last decade, implying that these are one of the reliable and commonly used biological model systems (Fig. 3)

Utility of lymphoblastoid cell lines for carcinogen sensitivity and DNA damage/repair studies
Of the total reports where LCLs have been used as a model system, a major segment of 44% is represented by carcinogen sensitivity (29%) and DNA damage/repair studies (15%) (Fig.4).

Limitations of using LCLs
Most of the above studies show LCLs as a good surrogate to study the effect of genotoxin   (Fig. 6). Therefore, care must be taken to ascertain the suitability of using LCLs in certain experiments and selecting the type of assay.

LCLs can be an ideal surrogate for lymphocytes (few other reports)
Although there are few studies where the utility of LCLs in place of isolated lymphocytes has   .7). We have used these LCLs for performing basic in vitro phenotypic assays like assessment of DNA damage/repair and cell death as well as cell cycle profiling after genotoxic exposure along with genomic DNA isolation (Fig. 8). The results that are obtained are promising and in concert with the published data, further strengthening our belief that LCLs can be an ideal substitute of peripheral blood cells.

Conclusions
The availability of continuously growing cell lines has markedly contributed to improvements in research and experimentation.
Foremost significance of cell lines lies in their ability to grow indefinitely and to be shared between groups which lead to more productive